The use of internal combustion engines pervades modern industrial society. Exhaust emission quality and fuel consumption efficiency are important aspects of operating such engines. The exhaust gas can contain unreacted fuel and combustion reaction byproducts which are harmful to the natural environment generally and especially to human health. If the engines are operated inefficiently, not only is more unreacted fuel emitted, but the amount of fuel consumed per unit of power produced increased. Because most internal combustion engines use nonrenewable, fossil fuels, excessively poor fuel consumption efficiency is undesirable. The finite sources are consumed more quickly and the natural environment is adversely impacted by the need to extract the less accessible sources. Poor fuel consumption efficiency also raises the cost of operating an engine.
Atmospheric air nominally contains about 79 volume % nitrogen and about 21 volume % oxygen. (The presence of various minor fractional components in air such as argon, carbon dioxide, ozone, and other air pollutants is recognized but is not germane to the present invention.) Air supplied to internal combustion engines produces nitrogen oxides, sometimes referred to as "NOx". These are undesirable components of engine exhaust emissions. Within limits, increasing the concentration of nitrogen fed to the engine can reduce the amount of NOx emitted.
Theoretically, refined or manufactured nitrogen can be blended with ambient air to increase the nitrogen concentration in the engine feed. For mobile engines, such as automobile, marine and portable generator gasoline and diesel fueled engines, providing a mobile supply of nitrogen has not been possible. Even for stationary engine installations, this technique is generally not practical.
A method that has been applied with some success for boosting the concentration of nitrogen in engine air involves the recirculation of exhaust gas. The exhaust gas is largely depleted of oxygen which has been consumed during combustion with the fuel and is enriched in nitrogen. By blending the exhaust gas with fresh air, the overall concentration of nitrogen is raised. Unfortunately, exhaust gas contains additional contaminants. These include particulates, carbon dioxide, carbon monoxide, volatile organic components from unreacted fuel and, of course, NOx. Particulates can be filtered, but filtration adds to the complexity of operating an engine. The filter ultimately will become blinded and itself becomes a source of waste requiring disposal or cleaning. The gaseous contaminants cannot be deemed to have a beneficial effect on engine performance or maintenance. Furthermore, a portion of the power of the engine must be used to filter and recycle the exhaust gas. It is thus desirable to have a plentiful source of nitrogen enriched air to enhance the concentration of nitrogen in internal combustion engine feed to reduce the amount of NOx in the exhaust. It is even more desirable that the source of nitrogen be portable.
Accordingly, the present invention now provides a method of operating an internal combustion engine with a plentiful and portable source of nitrogen enriched air. The novel method comprises the steps of:
(A) separating air into an oxygen enriched fraction and nitrogen enriched fraction with a selectively gas permeable membrane unit; and PA1 (B) feeding the oxygen enriched fraction or the nitrogen enriched fraction to the engine; PA1 (A) separating air into an oxygen enriched fraction and nitrogen enriched fraction with a selectively gas permeable membrane unit; and PA1 (B) feeding the oxygen enriched fraction to a combustion chamber of the engine; wherein the selectively gas permeable membrane unit includes a nonporous membrane (i) having an oxygen/nitrogen selectivity of at least 1.4 and a permeability to oxygen of at least 50 barrers; (ii) formed from an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole; and (iii) being at a temperature below the glass transition temperature of the amorphous copolymer. PA1 (a) a selectively gas permeable membrane unit including PA1 (b) pressure modification means for creating a negative pressure gradient across the membrane from a retentate cavity pressure to a permeate cavity pressure; and PA1 (c) a feed selection valve adapted to direct either oxygen enriched air or nitrogen enriched air to the combustion chamber.
wherein the selectively gas permeable membrane unit includes a nonporous membrane (i) having an oxygen/nitrogen selectivity of at least 1.4 and a permeability to oxygen of at least 50 barrers; (ii) formed from an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole; and (iii) being at a temperature below the glass transition temperature of the amorphous copolymer.
Certain aspects of internal combustion engine operation can be improved by feeding oxygen enriched air to the combustion chambers. One of these is reduction of cold start emission. That is, an engine started from a cold condition tends to burn fuel more inefficiently than normal until it achieves steady state operating temperature. The unburned fuel is emitted with the exhaust gas and contaminates the environment. Cold start emissions can be a significant source of air pollution, especially from automobiles.
The lean burn limit can also be improved by increasing the oxygen content of engine air. Again within limits, the ratio of fuel to air can be adjusted to obtain better fuel consumption efficiency. The leaner the fuel/air mixture, the better the economy. The higher limit of air to fuel ratio, the so-called lean burn limit, can be extended by boosting the concentration of oxygen in the air.
Thus it is sometimes desirable to supply internal combustion engines with oxygen enriched air. Exhaust gas recirculation is not a viable method of accomplishing this aim. However, the present invention does provide a method of operating an internal combustion engine with a plentiful and portable source of oxygen enriched air. The novel method comprises the steps of:
There is further provided according to the present invention an apparatus to feed enriched air to the combustion chamber of an internal combustion engine. The apparatus can be adapted to feed either nitrogen enriched air or oxygen enriched air. In one aspect the apparatus comprises:
a casing; and PA2 a nonporous membrane within the casing, wherein the membrane (i) has an oxygen/nitrogen selectivity of at least 1.4, and a permeability to oxygen of at least 50 barrers; (ii) is formed from an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole; and (iii) is at a temperature below the glass transition temperature of the amorphous copolymer; PA2 a retentate cavity within the casing on one side of the membrane, the retentate cavity being a source of a retentate stream flow of nitrogen enriched air produced by selective permeation through the membrane of oxygen from a feed stream flow of ambient air into the retentate cavity; and PA2 a permeate cavity within the casing on the opposite side of the membrane, the permeate cavity being a source of a permeate stream flow of oxygen enriched air; wherein the ratio of the permeate stream flow to the feed stream flow defines a stage cut; and
The aforementioned apparatus can be adapted to provide a continuously optimum feed concentration of either oxygen or nitrogen enriched air by the incorporation of a feedback control system. The feed back control system basically includes sensing means for detecting operating characteristics at selected locations in the apparatus and for converting the detected characteristics to machine readable signals, throttle means for adjusting the stage cut, and control means for evaluating the signals in accordance with a preprogrammed algorithm. The control means thus issue commands to the throttle means so as to make adjustments to the stage cut calculated to obtain improved operating characteristics.